Formation flying concept for bi-static SAR mapping of Titan surface

Multiple spacecrafts flying in close formation allow the effective implementation of single pass Synthetic Aperture Radar interferometry. Thanks to the separation of the orbiting vehicles along the cross-track direction, the derivation of the Digital Elevation Model (DEM) of the illuminated ground is enabled and, thanks to the separation in the alongtrack direction, the measurement of ground objects velocity (e.g. sea currents) is attainable. This technology has been recently and successfully implemented in Low Earth Orbit missions. The performances provided by the system in terms of mapping accuracy make of great interest the extension of this space segment architecture to interplanetary mission for mapping different celestial bodies. Attention is here focused on Saturn's moon Titan. Titan surface high accurate mapping is of great interest considering the presence of hydrocarbon lakes detected by Cassini-Huygens mission in the polar regions. In the framework of a phase A feasibility study, this paper proposes the methodology already applied to design formations around Earth as TanDEM-X and Prisma,1,2 to develop a suitable formation flying concept around Titan, compliant with the baselines constraints posed by the SAR interferometry, while minimizing the powered station and formation keeping maneuvers under a safe collision free design in proximity operations. The formation flying concept hereby presented stresses the smart exploitation of the natural perturbations affecting the dynamics around Titan for fuel saving, and comes out with a solution that provides big variety of baselines at all the latitudes and therefore high resolution and unambiguous DEM off the whole Titan surface. The specific strategy adopted to answer the mapping requirements with fuel consumption minimization is described in details, supported by the discussion of the obtained results.